View source for C-value

<p>The term <b>C-value</b> refers to the amount of <font color="#0645ad">DNA</font> contained within a <font color="#0645ad">haploid</font> <font color="#0645ad">nucleus</font> (e.g. a <font color="#0645ad">gamete</font>) or one half the amount in a <font color="#0645ad">diploid</font> <font color="#0645ad">somatic cell</font> of a <font color="#0645ad">eukaryotic</font> organism. In some cases (notably among diploid organisms), the terms C-value and <font color="#0645ad">genome size</font> are used interchangeably, however in <font color="#0645ad">polyploids</font> the C-value may represent two <font color="#0645ad">genomes</font> contained within the same nucleus. Greilhuber et al.<sup id="cite_ref-Greilhuber2005_0-0" class="reference"><font size="2"><font color="#0645ad"><span>[</span>1<span>]</span></font></font></sup> have suggested some new layers of terminology and associated abbreviations to clarify this issue, but these somewhat complex additions have yet to be used by other authors. C-values are reported in <font color="#0645ad">picograms</font>.</p>
<p>
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            <h2>Contents</h2>
            <span class="toctoggle"><font size="2">[</font><font color="#0645ad" size="2">hide</font><font size="2">]</font></span></div>
            <ul>
                <li class="toclevel-1 tocsection-1"><font color="#0645ad"><span class="tocnumber">1</span> <span class="toctext">Origin of the term</span></font></li>
                <li class="toclevel-1 tocsection-2"><font color="#0645ad"><span class="tocnumber">2</span> <span class="toctext">Variation among species</span></font></li>
                <li class="toclevel-1 tocsection-3"><font color="#0645ad"><span class="tocnumber">3</span> <span class="toctext">Calculating C-values</span></font></li>
                <li class="toclevel-1 tocsection-4"><font color="#0645ad"><span class="tocnumber">4</span> <span class="toctext">References</span></font></li>
                <li class="toclevel-1 tocsection-5"><font color="#0645ad"><span class="tocnumber">5</span> <span class="toctext">See also</span></font></li>
                <li class="toclevel-1 tocsection-6"><font color="#0645ad"><span class="tocnumber">6</span> <span class="toctext">External links</span></font></li>
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<h2><span id="Origin_of_the_term" class="mw-headline">Origin of the term</span></h2>
<p>Many authors have incorrectly assumed that the &quot;C&quot; in &quot;C-value&quot; refers to &quot;characteristic&quot;, &quot;content&quot;, or &quot;complement&quot;. Even among authors who have attempted to trace the origin of the term, there had been some confusion because Hewson Swift did not define it explicitly when he coined it in 1950.<sup id="cite_ref-Swift1950_1-0" class="reference"><font size="2"><font color="#0645ad"><span>[</span>2<span>]</span></font></font></sup> In his original paper, Swift appeared to use the designation &quot;1C value&quot;, &quot;2C value&quot;, etc., in reference to &quot;classes&quot; of DNA content (e.g., Gregory 2001<sup id="cite_ref-Gregory2001_2-0" class="reference"><font size="2"><font color="#0645ad"><span>[</span>3<span>]</span></font></font></sup>, 2002<sup id="cite_ref-Gregory2002_3-0" class="reference"><font size="2"><font color="#0645ad"><span>[</span>4<span>]</span></font></font></sup>); however, Swift explained in personal correspondence to Prof. Michael D. Bennett in 1975 that &quot;I am afraid the letter C stood for nothing more glamorous than 'constant', i.e., the amount of DNA that was characteristic of a particular <font color="#0645ad">genotype</font>&quot; (quoted in Bennett and Leitch 2005<sup id="cite_ref-Bennett2005_4-0" class="reference"><font size="2"><font color="#0645ad"><span>[</span>5<span>]</span></font></font></sup>). This is in reference to the report in 1948 by Vendrely and Vendrely of a &quot;remarkable constancy in the nuclear DNA content of all the cells in all the individuals within a given animal species&quot; (translated from the original <font color="#0645ad">French</font>).<sup id="cite_ref-Vendrely1948_5-0" class="reference"><font size="2"><font color="#0645ad"><span>[</span>6<span>]</span></font></font></sup> Swift's study of this topic related specifically to variation (or lack thereof) among <font color="#0645ad">chromosome</font> sets in different cell types within individuals, but his notation evolved into &quot;C-value&quot; in reference to the haploid DNA content of individual species and retains this usage today.</p>
<h2><span id="Variation_among_species" class="mw-headline">Variation among species</span></h2>
<div class="rellink boilerplate seealso">See also: <font color="#0645ad">C-value enigma</font></div>
<p>C-values vary enormously among species. In animals they range more than 3,300-fold, and in land plants they differ by a factor of about 1,000.<sup id="cite_ref-Bennett2005_4-1" class="reference"><font size="2"><font color="#0645ad"><span>[</span>5<span>]</span></font></font></sup><sup id="cite_ref-Gregory2005_6-0" class="reference"><font size="2"><font color="#0645ad"><span>[</span>7<span>]</span></font></font></sup> <font color="#0645ad">Protist</font> genomes have been reported to vary more than 300,000-fold in size, but the high end of this range (<i><font color="#0645ad">Amoeba</font></i>) has been called into question. Variation in C-values bears no relationship to the complexity of the organism or the number of <font color="#0645ad">genes</font> contained in its genome, an observation that was deemed wholly counterintuitive before the discovery of <font color="#0645ad">non-coding DNA</font> and which became known as the <font color="#0645ad">C-value paradox</font> as a result. However, although there is no longer any <font color="#0645ad">paradoxical</font> aspect to the discrepancy between C-value and gene number, this term remains in common usage. For reasons of conceptual clarification, the various puzzles that remain with regard to genome size variation instead have been suggested to more accurately comprise a complex but clearly defined puzzle known as the C-value enigma. C-values correlate with a range of features at the <font color="#0645ad">cell</font> and organism levels, including cell size, <font color="#0645ad">cell division</font> rate, and, depending on the <font color="#0645ad">taxon</font>, body size, <font color="#0645ad">metabolic rate</font>, developmental rate, <font color="#0645ad">organ</font> complexity, geographical distribution, and/or <font color="#0645ad">extinction</font> risk (for recent reviews, see Bennett and Leitch 2005<sup id="cite_ref-Bennett2005_4-2" class="reference"><font size="2"><font color="#0645ad"><span>[</span>5<span>]</span></font></font></sup>; Gregory 2005<sup id="cite_ref-Gregory2005_6-1" class="reference"><font size="2"><font color="#0645ad"><span>[</span>7<span>]</span></font></font></sup>.)</p>
<h2><span id="Calculating_C-values" class="mw-headline">Calculating C-values</span></h2>
<div>
<table class="wikitable">
    <caption>Table 1: Relative Molecular Weights of Nucleotides&dagger;</caption>
    <tbody>
        <tr>
            <th>Nucleotide</th>
            <th>Chemical formula</th>
            <th>Relative <font color="#0645ad">molecular weight</font></th>
        </tr>
        <tr>
            <td>2&prime;-deoxyadenosine 5&prime;-monophosphate</td>
            <td>C<sub><font size="2">10</font></sub>H<sub><font size="2">14</font></sub>N<sub><font size="2">5</font></sub>O<sub><font size="2">6</font></sub>P</td>
            <td align="right">331.2213</td>
        </tr>
        <tr>
            <td>2&prime;-deoxythymidine 5&prime;-monophosphate</td>
            <td>C<sub><font size="2">10</font></sub>H<sub><font size="2">15</font></sub>N<sub><font size="2">2</font></sub>O<sub><font size="2">8</font></sub>P</td>
            <td align="right">322.2079</td>
        </tr>
        <tr>
            <td>2&prime;-deoxyguanosine 5&prime;-monophosphate</td>
            <td>C<sub><font size="2">10</font></sub>H<sub><font size="2">14</font></sub>N<sub><font size="2">5</font></sub>O<sub><font size="2">7</font></sub>P</td>
            <td align="right">347.2207</td>
        </tr>
        <tr>
            <td>2&prime;-deoxycytidine 5&prime;-monophosphate</td>
            <td>C<sub><font size="2">9</font></sub>H<sub><font size="2">14</font></sub>N<sub><font size="2">3</font></sub>O<sub><font size="2">7</font></sub>P</td>
            <td align="right">307.1966</td>
        </tr>
    </tbody>
</table>
<p>&dagger;Source of table: Doležel <i>et al.</i>, 2003<sup id="cite_ref-Dolezel2003_7-0" class="reference"><font size="2"><font color="#0645ad"><span>[</span>8<span>]</span></font></font></sup></p>
</div>
<p>By using the data in Table 1, relative weights of nucleotide pairs can be calculated as follows: AT = 615.3830 and GC = 616.3711. Provided the ratio of AT to GC pairs is 1:1, the mean relative weight of one nucleotide pair is 615.8771 (&plusmn;1%).<sup id="cite_ref-Dolezel2003_7-1" class="reference"><font size="2"><font color="#0645ad"><span>[</span>8<span>]</span></font></font></sup></p>
<p>The relative molecular weight may be converted to an absolute value by multiplying it by the <font color="#0645ad">atomic mass unit</font> (1 u), which equals one-twelfth of a mass of 12C, i.e., 1.660539 &times; 10<sup><font size="2">-27</font></sup> kg. Consequently, the mean weight of one nucleotide pair would be 1.023 &times; 10<sup><font size="2">-9</font></sup> <font color="#0645ad">pg</font>, and 1 pg of DNA would represent 0.978 &times; 10<sup><font size="2">9</font></sup> base pairs.<sup id="cite_ref-Dolezel2003_7-2" class="reference"><font size="2"><font color="#0645ad"><span>[</span>8<span>]</span></font></font></sup></p>
<p>The formulas for converting the number of nucleotide pairs (or base pairs) to picograms of DNA and vice-versa are:<sup id="cite_ref-Dolezel2003_7-3" class="reference"><font size="2"><font color="#0645ad"><span>[</span>8<span>]</span></font></font></sup></p>
<pre>
genome size (bp) = (0.978 x 10<sup><font size="2">9</font></sup>) x DNA content (pg)
DNA content (pg) = genome size (bp) / (0.978 x 10<sup><font size="2">9</font></sup>)
1 pg = 978 Mb
</pre>
<p>The current estimates for human female and male diploid genome sizes are 6.406 &times; 10<sup><font size="2">9</font></sup> bp and 6.294 &times; 10<sup><font size="2">9</font></sup> bp, respectively.<sup id="cite_ref-IHGSC2001_8-0" class="reference"><font size="2"><font color="#0645ad"><span>[</span>9<span>]</span></font></font></sup> By using the conversion formulas given above, diploid human female and male nuclei in G<sub><font size="2">1</font></sub> phase of the <font color="#0645ad">cell cycle</font> should contain 6.550 and 6.436 pg of DNA, respectively.</p>
<h2><span id="References" class="mw-headline">References</span></h2>
<div class="references-small">
<ol class="references">
    <li id="cite_note-Greilhuber2005-0"><b><font color="#0645ad">^</font></b> <span class="citation Journal">Greilhuber J, Doležel J, Lys&aacute;k M, Bennett MD (2005). &quot;The origin, evolution and proposed stabilization of the terms 'genome size' and 'C-value' to describe nuclear DNA contents&quot;. <i>Annals of Botany</i> <b>95</b>: 255&ndash;260.</span><span class="Z3988" title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&amp;rft.genre=article&amp;rft.atitle=The+origin%2C+evolution+and+proposed+stabilization+of+the+terms+%27genome+size%27+and+%27C-value%27+to+describe+nuclear+DNA+contents&amp;rft.jtitle=Annals+of+Botany&amp;rft.aulast=Greilhuber+J%2C+Dole%C5%BEel+J%2C+Lys%C3%A1k+M%2C+Bennett+MD&amp;rft.au=Greilhuber+J%2C+Dole%C5%BEel+J%2C+Lys%C3%A1k+M%2C+Bennett+MD&amp;rft.date=2005&amp;rft.volume=95&amp;rft.pages=255%E2%80%93260&amp;rfr_id=info:sid/en.wikipedia.org:C-value"><span style="display: none">&nbsp;</span></span></li>
    <li id="cite_note-Swift1950-1"><b><font color="#0645ad">^</font></b> <span class="citation Journal">Swift H (1950). &quot;The constancy of deoxyribose nucleic acid in plant nuclei&quot;. <i>Proceedings of the National Academy of Sciences of the USA</i> <b>36</b>: 643&ndash;654.</span><span class="Z3988" title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&amp;rft.genre=article&amp;rft.atitle=The+constancy+of+deoxyribose+nucleic+acid+in+plant+nuclei&amp;rft.jtitle=Proceedings+of+the+National+Academy+of+Sciences+of+the+USA&amp;rft.aulast=Swift+H&amp;rft.au=Swift+H&amp;rft.date=1950&amp;rft.volume=36&amp;rft.pages=643%E2%80%93654&amp;rfr_id=info:sid/en.wikipedia.org:C-value"><span style="display: none">&nbsp;</span></span></li>
    <li id="cite_note-Gregory2001-2"><b><font color="#0645ad">^</font></b> <span class="citation Journal">Gregory TR (2001). &quot;Coincidence, coevolution, or causation? DNA content, cell size, and the C-value enigma&quot;. <i>Biological Reviews</i> <b>76</b>: 65&ndash;101.</span><span class="Z3988" title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&amp;rft.genre=article&amp;rft.atitle=Coincidence%2C+coevolution%2C+or+causation%3F+DNA+content%2C+cell+size%2C+and+the+C-value+enigma&amp;rft.jtitle=Biological+Reviews&amp;rft.aulast=Gregory+TR&amp;rft.au=Gregory+TR&amp;rft.date=2001&amp;rft.volume=76&amp;rft.pages=65%E2%80%93101&amp;rfr_id=info:sid/en.wikipedia.org:C-value"><span style="display: none">&nbsp;</span></span></li>
    <li id="cite_note-Gregory2002-3"><b><font color="#0645ad">^</font></b> <span class="citation Journal">Gregory TR (2002). &quot;A bird's-eye view of the C-value enigma: genome size, cell size, and metabolic rate in the class Aves&quot;. <i>Evolution</i> <b>56</b>: 121&ndash;130.</span><span class="Z3988" title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&amp;rft.genre=article&amp;rft.atitle=A+bird%27s-eye+view+of+the+C-value+enigma%3A+genome+size%2C+cell+size%2C+and+metabolic+rate+in+the+class+Aves&amp;rft.jtitle=Evolution&amp;rft.aulast=Gregory+TR&amp;rft.au=Gregory+TR&amp;rft.date=2002&amp;rft.volume=56&amp;rft.pages=121%E2%80%93130&amp;rfr_id=info:sid/en.wikipedia.org:C-value"><span style="display: none">&nbsp;</span></span></li>
    <li id="cite_note-Bennett2005-4">^ <sup><i><b><font color="#0645ad" size="2">a</font></b></i></sup> <sup><i><b><font color="#0645ad" size="2">b</font></b></i></sup> <sup><i><b><font color="#0645ad" size="2">c</font></b></i></sup> <span class="citation book">Bennett MD, Leitch IJ (2005). &quot;Genome size evolution in plants&quot;. In T.R. Gregory. <i><font color="#0645ad">The Evolution of the Genome</font></i>. San Diego: Elsevier. p.&nbsp;89&ndash;162.</span><span class="Z3988" title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&amp;rft.genre=bookitem&amp;rft.btitle=Genome+size+evolution+in+plants&amp;rft.atitle=%5B%5BThe+Evolution+of+the+Genome%5D%5D&amp;rft.aulast=Bennett+MD%2C+Leitch+IJ&amp;rft.au=Bennett+MD%2C+Leitch+IJ&amp;rft.date=2005&amp;rft.pages=p.%26nbsp%3B89%E2%80%93162&amp;rft.place=San+Diego&amp;rft.pub=Elsevier&amp;rfr_id=info:sid/en.wikipedia.org:C-value"><span style="display: none">&nbsp;</span></span></li>
    <li id="cite_note-Vendrely1948-5"><b><font color="#0645ad">^</font></b> <span class="citation Journal">Vendrely R, Vendrely C (1948). &quot;La teneur du noyau cellulaire en acide d&eacute;soxyribonucl&eacute;ique &agrave; travers les organes, les individus et les esp&egrave;ces animales&nbsp;: Techniques et premiers r&eacute;sultats&quot; (in French). <i>Experientia</i> <b>4</b>: 434&ndash;436.</span><span class="Z3988" title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&amp;rft.genre=article&amp;rft.atitle=La+teneur+du+noyau+cellulaire+en+acide+d%C3%A9soxyribonucl%C3%A9ique+%C3%A0+travers+les+organes%2C+les+individus+et+les+esp%C3%A8ces+animales%26nbsp%3B%3A+Techniques+et+premiers+r%C3%A9sultats&amp;rft.jtitle=Experientia&amp;rft.aulast=Vendrely+R%2C+Vendrely+C&amp;rft.au=Vendrely+R%2C+Vendrely+C&amp;rft.date=1948&amp;rft.volume=4&amp;rft.pages=434%E2%80%93436&amp;rfr_id=info:sid/en.wikipedia.org:C-value"><span style="display: none">&nbsp;</span></span></li>
    <li id="cite_note-Gregory2005-6">^ <sup><i><b><font color="#0645ad" size="2">a</font></b></i></sup> <sup><i><b><font color="#0645ad" size="2">b</font></b></i></sup> <span class="citation book">Gregory TR (2005). &quot;Genome size evolution in animals&quot;. In T.R. Gregory. <i><font color="#0645ad">The Evolution of the Genome</font></i>. San Diego: Elsevier. p.&nbsp;3&ndash;87.</span><span class="Z3988" title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&amp;rft.genre=bookitem&amp;rft.btitle=Genome+size+evolution+in+animals&amp;rft.atitle=%5B%5BThe+Evolution+of+the+Genome%5D%5D&amp;rft.aulast=Gregory+TR&amp;rft.au=Gregory+TR&amp;rft.date=2005&amp;rft.pages=p.%26nbsp%3B3%E2%80%9387&amp;rft.place=San+Diego&amp;rft.pub=Elsevier&amp;rfr_id=info:sid/en.wikipedia.org:C-value"><span style="display: none">&nbsp;</span></span></li>
    <li id="cite_note-Dolezel2003-7">^ <sup><i><b><font color="#0645ad" size="2">a</font></b></i></sup> <sup><i><b><font color="#0645ad" size="2">b</font></b></i></sup> <sup><i><b><font color="#0645ad" size="2">c</font></b></i></sup> <sup><i><b><font color="#0645ad" size="2">d</font></b></i></sup> <span class="citation Journal">Doležel J, Barto&scaron; J,Voglmayr H, Greilhuber J (2003). &quot;Letter to the editor: Nuclear DNA Content and Genome Size of Trout and Human&quot;. <i>Cytometry</i> <b>51A</b> (2): 127&ndash;128. <font color="#0645ad">doi</font>:<font color="#3366bb">10.1002/cyto.a.10013</font>. <font color="#0645ad">PMID</font>&nbsp;<font color="#3366bb">12541287</font>.</span><span class="Z3988" title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&amp;rft.genre=article&amp;rft.atitle=Letter+to+the+editor%3A+Nuclear+DNA+Content+and+Genome+Size+of+Trout+and+Human&amp;rft.jtitle=Cytometry&amp;rft.aulast=Dole%C5%BEel+J%2C+Barto%C5%A1+J%2CVoglmayr+H%2C+Greilhuber+J&amp;rft.au=Dole%C5%BEel+J%2C+Barto%C5%A1+J%2CVoglmayr+H%2C+Greilhuber+J&amp;rft.date=2003&amp;rft.volume=51A&amp;rft.issue=2&amp;rft.pages=127%E2%80%93128&amp;rft_id=info:doi/10.1002%2Fcyto.a.10013&amp;rft_id=info:pmid/12541287&amp;rfr_id=info:sid/en.wikipedia.org:C-value"><span style="display: none">&nbsp;</span></span></li>
    <li id="cite_note-IHGSC2001-8"><b><font color="#0645ad">^</font></b> <span class="citation Journal">Lander, ES; Linton, LM; Birren, B; Nusbaum, C; Zody, MC; Baldwin, J; Devon, K; Dewar, K <i>et al</i>. (2001). &quot;International Human Genome Sequencing Consortium. Initial sequencing and analysis of the human genome&quot;. <i>Nature</i> <b>409</b> (6822): 860&ndash;921. <font color="#0645ad">doi</font>:<font color="#3366bb">10.1038/35057062</font>. <font color="#0645ad">PMID</font>&nbsp;<font color="#3366bb">11237011</font>.</span><span class="Z3988" title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&amp;rft.genre=article&amp;rft.atitle=International+Human+Genome+Sequencing+Consortium.+Initial+sequencing+and+analysis+of+the+human+genome&amp;rft.jtitle=Nature&amp;rft.aulast=Lander&amp;rft.aufirst=ES&amp;rft.au=Lander%2C%26%2332%3BES&amp;rft.au=Linton%2C%26%2332%3BLM&amp;rft.au=Birren%2C%26%2332%3BB&amp;rft.au=Nusbaum%2C%26%2332%3BC&amp;rft.au=Zody%2C%26%2332%3BMC&amp;rft.au=Baldwin%2C%26%2332%3BJ&amp;rft.au=Devon%2C%26%2332%3BK&amp;rft.au=Dewar%2C%26%2332%3BK&amp;rft.au=Doyle%2C%26%2332%3BM&amp;rft.date=2001&amp;rft.volume=409&amp;rft.issue=6822&amp;rft.pages=860%E2%80%93921&amp;rft_id=info:doi/10.1038%2F35057062&amp;rft_id=info:pmid/11237011&amp;rfr_id=info:sid/en.wikipedia.org:C-value"><span style="display: none">&nbsp;</span></span></li>
</ol>
</div>
<h2><span id="See_also" class="mw-headline">See also</span></h2>
<ul>
    <li><a title="Animal Genome Size Database" href="/wiki/Animal_Genome_Size_Database"><font color="#0645ad">Animal Genome Size Database</font></a></li>
    <li><a title="Cell nucleus" href="/wiki/Cell_nucleus"><font color="#0645ad">Cell nucleus</font></a></li>
    <li><a title="Comparative genomics" href="/wiki/Comparative_genomics"><font color="#0645ad">Comparative genomics</font></a></li>
    <li><a title="C-value enigma" href="/wiki/C-value_enigma"><font color="#0645ad">C-value enigma</font></a></li>
    <li><a title="Genome" href="/wiki/Genome"><font color="#0645ad">Genome</font></a></li>
    <li><a title="Genome size" href="/wiki/Genome_size"><font color="#0645ad">Genome size</font></a></li>
    <li><a title="Human genome" href="/wiki/Human_genome"><font color="#0645ad">Human genome</font></a></li>
    <li><a class="mw-redirect" title="Junk DNA" href="/wiki/Junk_DNA"><font color="#0645ad">Junk DNA</font></a></li>
    <li><a title="Noncoding DNA" href="/wiki/Noncoding_DNA"><font color="#0645ad">Noncoding DNA</font></a></li>
    <li><a title="Plant DNA C-values Database" href="/wiki/Plant_DNA_C-values_Database"><font color="#0645ad">Plant DNA C-values Database</font></a></li>
    <li><a title="Selfish DNA" href="/wiki/Selfish_DNA"><font color="#0645ad">Selfish DNA</font></a></li>
    <li><a class="mw-redirect" title="Transposable elements" href="/wiki/Transposable_elements"><font color="#0645ad">Transposable elementsashkan</font></a></li>
</ul>
<h2><span id="External_links" class="mw-headline">External links</span></h2>
<ul>
    <li><a class="external text" href="http://www.genomesize.com" rel="nofollow"><font color="#3366bb">Animal Genome Size Database</font></a></li>
    <li><a class="external text" href="http://www.rbgkew.org.uk/cval/homepage.html" rel="nofollow"><font color="#3366bb">Plant DNA C-values Database</font></a></li>
    <li><a class="external text" href="http://www.zbi.ee/fungal-genomesize/index.php" rel="nofollow"><font color="#3366bb">Fungal Genome Size Database</font></a></li>
</ul>